Use your ult at
the start of a teamfight, as the first blows are struck, not at the
end. Not only does this make the enemy team less likely to be
aggressive, but it also allows your carries to get the kills rather
than you stealing them all later.

Stealing kills is bad because Zeus is mediocre in late game when nukes do less against high health pools, and BKBs are commonplace. Yes, Zeus has static field, but that's more about chip damage than serious wounds.

Ground-Targeting Lightning Bolt can check high ground, and also reveal hidden enemies. It's an under-used and highly useful application of the ability. You can also kill enemies by ground-targeting the lightning bolt - it actually has a 325 search range, and will hit the closest enemy in that area. You can also get extra range out of this (700 cast range + 325 search range).

How to Counter
Zeus

Items

Magic Stick/Wand: Zeus relies on spamming his spells, both in lane and in teamfights. You are almost guaranteed to get a ton of charges.

Buy a
Pipe. This is almost non-negotiable if you ever want to teamfight –
starting teamfights at half health is not fun.

Supports
buy cloaks / glimmer capes: it's almost always worth buying even just a "casual cloak" against Zeus. Even a L2 ult + L4 Lightning Bolt = 700 damage. A cloak brings you innate magic resistance from 25% to 36.25%, Instead of 525 dmg from the combo, you take 446, or 80 less damage - that's pretty good for a 550-gold item.

Smoke to
avoid Thundergod's Wrath when running away – it will reveal but not damage you if
you are “invisible”.

Blade mail
can be good if you are tanky, or are a high-priority target that
people tend to jump on. It may not save your life, but at least it
hurts Zeus!

Heroes

Gap-closers
with decent Hp are very good (Spirit Breaker good, Storm Spirit ok),

Burst
heroes (Skywrath, Spectre, Lina, QoP), to prey on squishy Zeus.

Silences
(Death Prophet, Drow, Skywrath, etc)

Pugna,
because Zeus wants to be able to spam his spells without getting
zapped.

Anti-mage, 'cause... he's an anti-magic hero.

Tactics

Gank him
frequently, especially if he goes mid. He has no escape or stun,
and only gets stronger once he has items (mana regen, mobility, hp)

If you
find that teamfights aren’t quick, decisive affairs, try targeting
Zeus earlier, so he can’t spam his spells.

Jumping on
Zeus and killing him before he can ult greatly increases your
chances of teamfight success.